Car's VSS sensor (Vehicle Speed Sensor)

Status
Not open for further replies.

ikalogic

Member
Hello everybody...

I am now working in a brand new french company called FILMARIANE. We build GPS/GPRS tracking system for luxury cars.

One of the functionalities of the device we are building is to detect the distance traveled by the car. For that, we decided to plug our device on the speedsensor wire.

I have build a circuit that converts any oscillating signal, square or sinus shaped, to 5V pulses that is fed directly to our embedded electronics. I am hoping that this circuit would be compatible with any type of sensor that is mount in the different vehiculs on the market.

I have litle knoledge in the world of automobile industry, and i was hoping to know, if by an change you would know, if all (or almost all) speed sensors provide oscillating electrical signals. My doubt come from some posts on the net that says that some sensors output a voltage proportional to speed, Is that true?

If yes i would have to take that into consideration to make to device compatible with more cars on the market.

If It's not too much to ask, does all recent vehicle also have this VSS signal available somewhere, or do I have to get the information via a data bus (CAN, etc...)?

If this can help, i am talking about the VSS signal that TaxiMeters use to count displacement...


Thanks for giving any information
 
Last edited:
There is 2 Vss signals, both wrongly named Vss (vehicle speed sensor) , misused by the vast majority of people talking about the subject.

There is one signal outputted by the driveshaft sensor, can be whatever number depending on manufacturer, year, and model. From 4 pulses per shaft revolution to 44 as far as I know.

That signal is fed to the onboard compfuser or DRAC (digital ratio adapter controller) and is divided -or not- to feed the speedometer. That divided signal is also wrongly called Vss, and is meant to be usually 1000 pulses per mile in USA.

Changing tire sizes, differential ratios, etc, changes the pulses per mile and different gears have to be installed in the sensor to retain accuracy.

Newer model cars do provide a fixed signal in a pin coming out of the compfuser to be used in whatever external application, but do not expect a standard...

Miguel
 
Last edited:
I don't really know about the "voltage proportional to speed" type of systems, so am unable to comment.

Regarding the vehicles I come into contact with usually, a pulse type system is normally employed and utilises the ABS wheel speed sensors, along with the steering angle sensor, to calculate road speed. Since the outer wheels rotate faster than the inner wheels during a turn, steering angle has to be taken into account and some form of averaging takes place. No single wheel speed sensor can be relied upon as a true indicator of speed, unless the vehicle is travelling in a straight line, with no slippage (Read: Wheel-spin or brake lock-up) The system uses a fixed number of pulses from the ABS wheel speed sensors and a programming option, to cater for differing tyre circumference, to allow for the numerous tyre sizes offered throughout the vehicle range.

Normally, there is an output from the ABS control module, either via a dedicated VSS wire or over the CAN-Bus. Usual places that the vehicle speed signal is routed to are:
ECM - Engine Control Module (Also known as PCM - Powertrain Control Module)
Instrument cluster - Quite obviously..
Radio/Infotainment module - Speed dependant volume control is common-place these days.
And lastly, but something that should not really be tapped into...The SRS (Safety Restraint System)

I'm afraid that the above info could be too manufacturer-specific to be applied as a steadfast rule to most makes, so the best option I can suggest, is to maybe subscribe to Autodata, where you would have access to info for a large number of makes, along with telephone support for those that haven't made the latest release.


HTH.
 
Do you need to use the Vss at all?, why not just calculate the distance travelled from the GPS data?.
 

Thanks a lot for your message, So as far as i understand, in most car there will be a signal that oscillates to indicate displacement, right?

Actually the device will be sold to specialists that will mount them in the vehicles, so i am not worried about "finding the right VSS wire", that's their job.

What i am worried about is to develop a device than can read the signal from all the standards.

Also, about the number of pulses per turn or wheel diameter or whatever parameter, that's not a problem at all, the program is auto adaptive by comparing the counted pulses with the data taken from the GPS.

As i said again i have build an input stage that will take any kind of oscillating voltage (AC or DC, Square or sin wave, 1V Peak to Peak up to 12V peak to peak) and output a clean TTL square wave.

So, let me reformulate my question, is there in most cars, a signal that oscillates with respect to displacement (regardless of the frequency, voltage, or wave shape) ?

Thanks for your time again...

NB: we dont need to target 100% of the market, I just want to be sure that the solution is quite standard, and/or equivalent to the one used by Taximeter
 
Last edited:
Nigel Goodwin said:
Do you need to use the Vss at all?, why not just calculate the distance travelled from the GPS data?.
Click to expand...

we cannot afford the errors due to signal losses that may happen under bridges or in tunnels... so we have to compensate with another source of information
 
ikalogic said:
we cannot afford the errors due to signal losses that may happen under bridges or in tunnels... so we have to compensate with another source of information
Click to expand...

True. But for example, in Chicago here where i live, theres a LOT of underground tunnels and streets that don't see the surface for a few miles. Theres actually a few streets you can turn to while still underground.

How can you know where the person is going if he turns underground just by reading the vehile speed? Or are you planning on implementing an actual sensor to also know when they are turning and by how many degrees?
 


The idea is not to track the user underground, no, the idea is that if we lose the position, at least we do not loose the distance measurement, as this information (regardless of the position) is used for other reasons...
 
Here's what you could do and it should work for all cars:

Take the speedometer feed line and analyse that. Since the signal being fed to it can vary based on cars, all you would have to do is get the car from lets say 0 to 10 mph (or km) and see how the signal changes. This data can be processed inside your device. How will you know when it reaches some speed? Simple. You have a GPS on-board. Use it for that purpose.

In other words "learn" the speedometer feed signal:
1. Connect to speedometer.
2. Take signal reading while car is running with a GPS signal.
3. Record values at different speeds to determine how signal is being fed to the speedometer.
So your GPS would record the speed of the vehicle based on satellites (this can be quite accurate to be honest). Take a reading of the speed and pulses for the speedometer. Divide the pulses by speed, find pulses/mile. Therefore, knowing this information, you can easily tell how fast the car is going even if the GPS doesn't have a signal.

Would this work?
 
On OLD cars, it is rare to find a VSS signal, although my 20 year old bmw has one, on modern cars it can be found either on pin 1 of the ISO connector behind the radio or behind the speedo head. If your getting a voltage proportional to speed, it means that you tapped the wire before processing by the ECU, one of the other wires coming from the ECU will have a nice square wave proportional to speed. (could be 5v, could be 12v - depends on the vehicle)

NEW cars that have CAN enabled systems generally do not have a vss wire, but some do (toyota avensis, ford mondeo (MK3), etc)

It would appear though that you are trying to re-invent the wheel.

The type of people who would fit this gizmo for you will already have a source of convertors to use with your system. I just flicked though my files and found 12 different suppliers who I deal with regularly who can supply adaptors for ANY car on the market to a nice square wave pulse. They have adapters that clip on the mechanical speedo cables, they have CAN adapters, they have sensors with magnets for when nothing else works, that you attach to a driveshaft/propshaft.

I personally think you should just concentrate on making your gizmo, as there are already enough places that can supply the interface from a car to it. Plus you will be spending a load of cash making adapters that could be spend better else where - as some of your customers cars will need one, some wont, some will be can, others wont.

(Im a taximeter installer btw)
 

Thanks for the response.

To take back your words, i am trying "not" to reinvent the wheel. I am trying to do the strict minimum so that installers can easily install the device on most cars. I also figured out that if a specific car need more specific equipment to get the VSS signal, then he would figure out what need to be added.

In other words, i am trying to make a solution that is as standard as taximeters, so, let me re-re-formulate my question!! : taximeters need the VSS signal to function, then it's up to the specialist installer (like you) to figure out if the VSS line on that car need some conditioning or adapting? right?
And just to make sure we are talking about the same thing, the VSS signal that taximeters need is a PULSE signal, not a variable voltage right?

I would be very thankful if you could provide me with a sharp "yes/no" answer to those two questions. (an answer from a taximeter installer would be very reassuring! )
 
All taximeters (that I have ever dealt with) expect to recieve a square wave pulse input, the meters are tolerant of both 5v and 12v signals.

The meters will accept either a 5v/gnd, 12v/gnd or float/gnd input (i believe the last case is handled with a diode to prevent backfeed and a pullup resistor inside the meter. (when looking at the circuit with a testlamp in the last case you get GND_No Connection_GND_No Connection etc on the pulse wire.

No meter I have ever dealt with works directly with the analogue varying voltage from the speed sensor.

when we get cars in, we buy a meter from one of our suppliers, and it is our job to put in whatever adapters as neccessary to generate a nice plulse for the meter. In some cases this would include adding new sensors, pull-ups - neccessary for cars using abs sensors for speed, as the floating signal doesnt get pulled high fast enough - on these vehicles things work fine till about 50mph, then stop working at all unless an external pull-up is used.

From your side I would think your gizmo needs to handle the three pulse types above. Then the car is driven over a measured mile, dont know what the situation around the world is, but in the UK - EVERY local county has at least one 'Official' measured mile - its what the police cars use to calibrate there systems. anyway you reset the count at the beginning, drive the mile and record the count at the end. It can be anywhere from approx 1000 pulses to over 100,000 pulses. Store this in your system and use it for calculating distance, speed, etc.

hope this helps

yes/no answers

does your system need to handle analogue variable voltage NO

does you system need to handle the 3 pulsed arrangements above YES

will a professional installer be able to fit your product to ANY car, YES if the condition above is satisfied.
 


Thanks a lot for your time. I don't know how to thank you.

best regards from France, Limoges!
 
My speedometer and odometer are dead. I read that the problem can relate to a dead vehicle speed sensor (VSS). I looked under the engine, under the tranny, and couldn't find where the VSS is located. If the VSS is dead, then shouldn't the check engine light turn on?. For my car, there is no check engine or any light turn on.
 
Status
Not open for further replies.

Similar threads

G
  • Question
LED Flood Light PIR sensor upgrade
Replies
6
Views
730
Diver300
D
  • Question
Infrared sensor array to detect mosquito entry
Replies
11
Views
3K
Externet
F
Hall sensor problems.
Replies
7
Views
1K
fil
F
O
  • Solved
Two types of resolution of a sensor
Replies
2
Views
1K
Otto_
O
K
  • Question
LM3914 Temperature Sensor LM62 help please
Replies
6
Views
2K
k11m08
K
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…